Variable gain vehicle speed control system

ABSTRACT

An automotive speed control system employs a speed analog voltage generator that has a linear speed-voltage characteristic. The throttle position control voltage used to close the system&#39;&#39;s throttle control servomechanism loop is made to produce a d-c voltage directly proportional to throttle advance. This arrangement provides a large dynamic control range at all vehicle speeds. Systems gain is varied in proportion to vehicle speed to provide a psychologically satisfactory dynamic performance at all speeds.

United States Patent Seidler et a1.

[ May 27, 1975 VARIABLE GAIN VEHICLE SPEED 3,580,355 5/1971 Kitano 180/105 E CONTROL SYSTEM 3,582,679 6/1971 Carp 180/105 E X 3,599,052 8/1971 Carp 180/105 E X 1 Inventors: Helmut Seldler, Schwenksvflle; 3,648,798 3/1972 Jania 180/105 E James T. Walker, Norristown, both of Primary ExaminerDavid Schonberg [73] Assignee: Philco-Ford Corporation, Blue Bell, Asslsmnt Exammer Terrance Slemens Pa Attorney, Agent, or FzrmRobert D. Sanborn; Gall W. Woodward [22] Flledz Dec. 10, 1973 [21] Appl. No.: 423,549 [57] ABSTRACT An automotive speed control system employs a speed 52 us. (:1. 180/105 E; 123/102 analog voltage generator that has a linear Speed- 51 Int. Cl B60k 31/00 voltage haracteristic- The thmflle POsition Control [58] Field of Search 180/105 E 123/102 voltage used to close the systems throttle control ser- 123/103 vomechanism loop is made to produce a d-c voltage directly proportional to throttle advance. This ar- [56] References Cited rangement provides a large dynamic control range at UNITED STATES PATENTS all vehicle speeds. Systems gain is varied in proportion to vehicle speed to provide a psychologically satisfacgeapomakls tory dynamic performance at all speeds. arp 3,575,256 4/1971 .lania 180/105 E 2 Claims, 2 Drawing Figures 6.2 rau 2w:

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70 7111 555; L .w/r ffliiflflA/ifl? VACUUM VARIABLE GAIN VEHICLE SPEED CONTROL SYSTEM BACKGROUND OF THE INVENTION Automatic vehicle speed controls have evolved from simple fluid servomechanisms into electronicallyamplified electromechanical systems having sophisticated control characteristics and high reliability. A typical prior art electronic system employs a high quality low leakage capacitor as a memory element. The capacitor charge represents an analog of the desired vehicle speed. An analog voltage generator, coupled to the vehicle speedometer shaft, produces a voltage proportional to vehicle speed. These two analogs are compared and the difference amplified and used to operate an electromechanical device that is connected to the throttle of the vehicle engine. Analog voltage generators in the prior art have been notable for their nonlinearity. The output typically increases to a lesser extent at high outputs than the output would increase for the same input change at low outputs. To compensate for this effect, prior art systems typically vary the system gain, by increasing the gain at high speeds, so that the overall system will have a linear response. The nature of the control system in these prior systems make it desirable that the servomechanism operate from a throttle position feedback that produces a voltage that decreases with advancing throttle. The system gain is varied by altering the throttle position feedback in such a manner that the overall speed control servomechanism response is constant at all vehicle speeds. Unfortunately, this combination severly reduces dynamic range at the higher speeds.

SUMMARY OF THE INVENTION It is an object of the present invention to produce a vehicular electronic speed control system that has performance characteristics more nearly approximating those desired by a human operator.

It is a further object to provide a variable system gain function in a vehicular electronic speed control system that provides a control characteristic that is more ac ceptable to a human operator.

These and other objects are achieved by employing a typical prior art speed control system with the following alterations. An analog speed voltage generator having a linear relationship between speed and voltage is employed in place of the usual non-linear device. The throttle position analog voltage generator is arranged to produce a d-c voltage that is directly proportional to throttle advance. These measures provide a large system dynamic range at all speeds. The throttle position voltage is modulated by the speed analog voltage so that a slightly reduced throttle position voltage range occurs at higher vehicle speeds. This results in higher speed control servomechanism gain at higher speeds thereby to provide a more psychologically pleasing system response.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagram of a speed control system using the invention; and

FIG. 2 is a schematic diagram of the electronic and electromechanical portions of the speed control system of FIG. 1.

DESCRIPTION OF THE INVENTION FIG. 1 is a block diagram of the complete speed control system showing the various control links. The vehicle 1 is powered by an engine 2 that is controlled by throttle 3. The vehicle speedometer 4 is typically operated from a rotary shaft. The shaft information is converted to an analog voltage in the speed analog voltage generator 5. This circuit is designed to produce a d-c voltage that is linearly proportional to actual vehicle speed. The desired vehicle speed is inserted as an analog voltage into a memory device 6. This is usually a high-quality low-leakage capacitor that is charged to the desired speed analog voltage by the speed set circuits 7. These circuits also contain the control function provisions for coast and accelerate operation. A comparator 8 senses the relationship between the actual speed and desired speed analog voltages and produces a difference output that is positive when the speed analog voltage predominates. In effect the desired speed analog voltage is subtracted from the speed analog voltage. The comparator output is amplified by differential amplifier 16 and control amplifier 9 which in turn operates throttle actuator 10. The throttle actuator 10 is mechanically coupled to the throttle 3. This completes a closed servo control loop for the vehicle speed.

When the speed analog voltage is too high the system will, through the action of throttle actuator 10, reduce throttle and slow the vehicle. When the speed analog voltage is too low, the system, through throttle actuator 10, will advance the throttle and increase vehicle speed. Thus, as road and wind conditions, and other variables, tend to vary vehicle speed, the system will operate the throttle to maintain a constant speed.

The vehicle throttle must operate about a position that is a function of the desired vehicle speed. The initial speed control link provides this initial speed voltage which is simply a fraction of the analog speed voltage. The speed analog voltage is fed through an attenuator 11 (to establish the desired fraction) to the noninverting differential amplifier 16 input. This voltage is inserted into the system so that throttle position, as set by the throttle actuator, is directly proportional to the actual vehicle speed.

In order to stabilize the system, the initial speed voltage must be balanced by a voltage that represents the actual throttle position. To accomplish this, a throttle position voltage control '12 is operated from throttle actuator 10. This device generates a d-c voltage directly proportional to throttle advance. A fraction of this voltage is'fed to the inverting input of differential amplifier 16 through attenuator 13. Thus a second complete servo control loop is formed and this loop will position the throttle to stabilize it where it will produce the actual vehicle speed. In terms of a human driver, this corresponds to holding the accelerator at that fixed location that represents the vehicle speed.

In order to make the system more responsive or adaptable to changes in speed, a differentiator 14 parallels attenuator 13. This makes the throttle position control loop more sensitive to changes in throttle position than it is to fixed position. This gives the control system a fast response to changing conditions while maintaining the desired stable response to fixed conditions.

Finally, a speed gain control link 15 is connected between the speed analog voltage control generator 5 and throttle position voltage control 12. This link is present because, in operating a vehicle, a psychological factor becomes perceptible. 1f the system has constant fixed speed control responses it seems as if the control is more sluggish at high speeds. This is thought to be due to the observation that at high speeds a driver is less sensitive to a given speed change. Accordingly, to provide a more satisfying speed control characteristic the system gain is made to increase with speed. This means that a lesser actual speed change is required to move the throttle from idle to maximum at higher speeds. In the system to be described in detail subsequently the vehicle speed change required to move the throttle from idle to maximum is varied at 3.8 mph. at 30 mph. to 3.2 mph. at 85 m.p.h. In prior art systems, using a constant system gain, satisfactory performance at high speed resulted in seemingly jerky low speed performance. If the gain were optimized at low speed, the system seemed to be sluggish at high speed.

FIG. 2 is a schematic diagram illustrating the electronic and electromechanical elements of FIG. 1. Throttle actuator is coupled to the throttle by way of the accelerator pedal and the usual mechanical linkages. Return spring 21 provides the usual restoring force that returns the vehicle engine to idle in the absence of a force applied to the accelerator or its linkages.

Actuator 10 includes an output shaft 22 which when retracted will pull the accelerator pedal 20 toward the floorboard and advance the throttle. Shaft 22 is fastened to flexible diaphragm 23 which acts as a sealed off closure for chamber 24. Chamber 25, on the other side of diaphragm 23, operates at atmospheric pressure by virtue of vent 26. Compression spring 27 will, in the absence of other forces, push diaphragm 23 in a direction that will extend shaft 22 to its maximum. This position is such that it will slightly exceed the idle position of the throttle.

Chamber 24 has two plunger-operated vents. Vent 30, which communicates with the atmosphere, is normally open. It can be closed by means of plunger 31 which is actuated by coil 33. Plunger 31 is normally held away from vent 30 by spring 32. As long as vent 30 is open spring 27 will dominate and shaft 22 will be at maximum extension. Vent 34 is coupled by means of a conventional flexible hose to a conventional vacuum reservoir (not shown). This vent is normally closed by plunger 35 due to the action of spring 36. When coil 37 is energized, plunger 35 will be forced back against spring 36 thus opening vent 34.

If vent 30 is closed by energizing coil 33 and vent 34 opened by energizing coil 37, chamber 24 will be evacuated and flexible diaphragm 23 will be acted upon by the air pressure in chamber thereby causing it to compress spring 27 and retract shaft 22. At full vacuum in chamber 25 shaft 22 will be retracted sufficiently to advance the throttle to maximum. Since actuator 10 involves a relatively large chamber 24 supplied through relatively small vents, the movement of shaft 22 is rapid but not undesirably so. Its speed of action is adjusted by controlling vent bore to provide smooth throttle control that can be halted at a suitable point.

If while vent is closed, vent 34 is opened long enough to retract shaft 22 only part way and then is closed again, the constant reduced pressure inside chamber 24 will hold shaft 22 in that fixed position.

Thus, to summarize the action of actuator 10, when both coils are deenergized shaft 24 will move to the idle position. If both coils are energized, shaft 22 will advance toward the maximum throttle position. If coil 33 is energized alone, shaft 22 will hold whatever position it had at the instant coil 37 became deenergized.

Transistors 40 and 41 are connected to energize coils 33 and 37 in the following manner. Coil 33 is connected between the collector of transistor 40 and the battery supply. Coil 37 is connected between the collector of transistor 41 and the battery supply. Thus when either transistor is turned on, the respective coil will operate the related plunger. The emitter of transistor 40 is grounded while the emitter of transistor 41 is returned to the collector of transistor 40 through diode 43. The bases of transistors 40 and 41 are connected together by base current limiting resistor 42. This mode of connection means that transistor 40can conduct without transistor 41 conducting, but transistor 41 cannot conduct unless transistor 40 is also conducting.

The operation of these transistor circuits will now be described in relation to circuit point 46. If circuit point 46 is at ground potential neither transistor 40 nor 41 will conduct and coils 33 and 37 will be deenergized. Accordingly, shaft 22 will be at maximum extension or idle position. If the voltage at point 46 rises in a positive direction to about 0.7 volt, transistor 40. willstart .to conduct and at some level slightly above about 0.7 volt. coil 33 will be energized thus closing vent 30. When transistor 40 becomes saturated the voltage at its collector will be about 0.2 volt. As the voltage at point 46 is increased still further, a point will be reached where transistor 41 will begin to conduct. This will occur at about 1.5 volts. This includes the 0.2 volt across tran sistor 40, the 0.6 volt value needed to forward bias diode 43, and the 0.7 volt required to turn the baseof transistor 41 on. At some point slightly above this volt.- age, coil 37 will be energized and vent 34 will be opened, thus causing shaft 22 to retract.

Three conditions are therefore available in response to the voltage at point 46. In the first, below about 0.7 volt, vent 311 is open, vent 34 closed, and shaft 22 will move toward idle. In the second condition in the range of about 0.7 to 1.5 volts, vents 30 and 34 are both closed and shaft 22 held in whatever position it was in when this condition was established. Above 1.5 volts, both coils will be energized, thereby opening vent 34 while vent 30 remains closed. The vacuum thus created:

in chamber 24 will cause shaft 22 to retract and move the throttle toward its fully advancedposition.

Diodes 44 and 45 are connected across coils 33 and 37 respectively. These diodes are poled so as to be reverse biased when the coils are energized, and will have no effect upon the energized coils. When either transistor 40 or 41 is turned off the inductive kick-back developed .in the associated coil will forward bias the related diode and thus be absorbed. These diodes therefore serve as protective devices to prevent excessive collector voltage appearing at the transistor collectors.

The voltage at point 46 is controlled through the agency of a two stage cascade amplifier which is driven from a differential amplifier in response to the voltage at circuit reference point 47. These amplifiers are all direct coupled and arranged so that point 46 operates in the opposite sense from point 47. Thus if point 47 is at a high positive potential, point 46 will be at a low positive potential. The operation of the direct coupled amplifiers is as follows.

Transistor 50 is a common emitter stage, the output of which is directly connected to circuit point 46. Resistor 51 constitutes the collector load resistor and is connected to the automobile battery circuit. Resistors 52 and 53 provide in part the base bias for transistor 50 and provide for negative feedback to stabilize the stage gain and operating point. Capacitor 54 is connected as a low frequency pass element that limits the maximum circuit operating frequency, or it could be characterized as controlling the servo slew rate.

Resistor 55 connects the base of transistor 50 to the vehicle brake light circuit. When the brake light is off, as it is normally, resistor 55 is in series with the brake lamp circuit and the series combination will be in parallel with resistor 53. The values are adjusted so that transistor 50 operates as a conventional common emitter amplifier. However, when the brake light is actuated by depressing the vehicle brake pedal, a positive voltage of about 12 to 14 volts appears at the lower end of resistor 55. The value of resistor 55 is selected in conjunction with the base bias resistors to saturate transistor 50 when the brake light is actuated. This drives circuit point 46 to about 0.2 volt, thereby deenergizing both coils 33 and 37 to allow shaft 22 to fully extend and return the throttle to idle. This circuit ensures that when the vehicle brake is operated, the effect of the speed control is immediately cancelled. In related circuits, not shown, the same brake-pedalproduced voltage is used to de-energize the entire speed control circuit. To return to the speed control back to mode, the circuit would have to be deliberately turned on or reenergized.

Transistor 56 constitutes a common emitter amplifier directly coupled to transistor 50. Resistor 57 along with the base circuit of transistor 50 constitutes the collector load for transistor 56. Base resistors 58 and 69 directly couple the input of transistor 56 to the output of a differential amplifier.

Transistor 59 and 60 constitute a conventional differential amplifier 16. Resistor 61 is the common emitter coupling element, resistor 62 is the output load resistor, and resistor 63 is the circuit balancing load resistor. Resistors 64 and 65 form a voltage divider that establishes in part the base bias on transistor 60. Resistors 66 and 67 form a voltage divider that establishes in part the base bias on transistor 59. Resistor 66 is collector-base connected to provide negative feedback to stabilize the differential amplifier 16. Resistor 68 directly couples the input of the differential amplifier 16 to circuit point 47.

Potentiometer 70, which supplies a variable voltage to the inverting input of the differential amplifier 16, has its variable arm coupled mechanically to shaft 22 on actuator as shown by the dashed line. The mechanical linkages are arranged so that when shaft 22 is at maximum extension, or idle position, the arm of potentiometer is at its lower extreme. As shaft 22 is retracted, the arm will move toward the upper end of potentiometer 70. Together with resistors 71 and 72, potentiometer 70 forms a voltage divider connected from the 8.2 volt line to ground. The 8.2 volt line is established by zener diode 73 and resistor 74 from the automobile battery circuit. Accordingly, as shaft 22 is retracted, the positive voltage at the arm of potentiometer will increase in direct proportion, i.e., said voltage is directly proportional to throttle actuation.

The voltage at the arm of potentiometer 70 is coupled to the base of transistor 59 by way of two separate elements. Resistor provides direct coupling and, in conjunction with the base circuit resistors of transistor 59, acts as a fixed attenuator. (See element 13 of FIG. 1.) Resistor 81 is combination with capacitor 82, along with the base circuit resistors of transistor 59, provides for increased a-c coupling and the effect is a differentiator connected between the arm of potentiometer 70 and the base of transistor 59. (See element 14 of FIG. 1.) This combination of attenuator and differentiator coupling gives the coupling one gain value for steady state and a higher gain value for transient or changing conditions.

Thus, the combined action of the differential amplifier and two common emitter cascaded states of amplification, all of which are directly coupled, provide amplification with 180 phase shift (or one inversion) between circuit points 47 and 46. In addition, the d-c operating point of amplifier system is varied with the action of potentiometer 70.

The voltage at circuit point 47 is primarily determined by the conduction of insulated-gate field-effect transistor (IGFET) 85. Resistor 86 constitutes the load in a gate-follower circuit. The actual voltage at point 47 depends upon the characteristics of the particular IGFET being used and the voltage at its gate electrode. The gate voltage will be determined by the charge upon capacitor 87 and the voltage at circuit point 88. The capacitor charge is initially established with the aid of control circuit (not shown in FIG. 2, but represented in FIG. 1 by block 7) to represent an analog voltage proportional to the desired vehicle speed. The voltage at point 88, which is established by a circuit to be described subsequently, is an analog of the actual speed of the vehicle. The nature of the comparison circuit including capacitor 87, the control circuits, and the IGFET are taught in detail in co-pending application Ser. No. 414,199 filed Nov. 9, 1973. This application is hereby included for its teaching by reference.

The circuits associated with transistors 90, 91, and 92 are taught in detail in the US. Pat. to Bozoian No. 3,613,820. Accordingly, this portion of the circuit will not be described in great detail. Transducer 93, which is driven mechanically from the vehicle speedometer shaft, produces an a-c signal having a frequency that is directly proportional to vehicle speed. Transistor 90, along with its base resistor 94, collector load resistor 95, and feedback capacitor 96, produces a constant output amplitude square wave of transducer 93 frequency. Capacitors 97 and 98 along with diode 99 comprise a frequency counter, with the charge on capacitor 98 being proportional to frequency. Transistor 91 is connected to control the voltage on capacitor 98 so that it is a linear function of frequency. Resistors 101 and 102 along with diode and thermistor 103 provide for temperature compensation of the vehicle speed analog voltage at point 88. Capacitor 104 and resistor 105 act to filter any ripple in the voltage across capacitor 98. Transistor 92 is an emitter follower in which resistors 106 and 72 comprise the d-c load. Capacitor 107 is the a-c load bypass. A portion of the voltage at point 88 is coupled by way of a resistive voltage divider (comprising resistors 108 and 65) to the noninverting input of the differential amplifier, i.e., to the base of transistor 60.

By virtue of the operation of transistors 90, 91, and 92, the voltage at point 88 will be a positive d-c voltage having an increment of about 75 mv per m.p.h. This speed analog voltage is applied to the left hand plate of capacitor 87. The charge on capacitor 87, i.e., the desired speed analog voltage, is established by the control circuits as taught in the co-pending application Ser. No. 414,199. The capacitor charge is subtracted from the potential at point 88 and the difference appears at the gate electrode of IGFET 85. In accordance with the characteristics of IGFET 85 the gate voltage appears as a positive potential at point 47. The control circuits are set up at manufacture so that the voltage at point 47 when translated through the amplifiers to point 46 will produce a voltage in the range of 0.7 to 1.5 when the vehicle speed equals the desired speed. As described above, this condition will cause actuator 10 to hold shaft 22 fixed. The extension or position of shaft 22 will therefore be a function of the voltage at point 88.

If the vehicle speed were to increase, for example by virtue of a downgrade, the voltage at point 88, and hence the voltage at point 47, will go more positive and the voltage at point 46 less positive. If the voltage at point 46 drops below about 0.7 volt, due to sufficient speed change, actuator 10 will cause shaft 26 to extend thereby reducing the throttle and vehicle speed. When the desired speed is again achieved and the voltage at point 46 returned to about the 0.7 to 1.4 volt range, the actuator 10 will again hold shaft 22 fixed.

If the vehicle speed were to decrease, for example by virtue of an upgrade, the voltage at point 88, and hence the voltage at 47 will drop. Due to the amplifiers, the voltage at point 46 will increase. If the increase exceeds about 1.5 volts, actuator 10 will cause shaft 22 to retract thereby advancing the throttle until the desired speed is again achieved.

A concept of system gain can be established in terms of how much vehicle speed change is required to fully advance the throttle. This number in m.p.h. is typically about 3.5. In terms of analog speed voltage this would be about 260 millivolts. Since the voltage at point 46 would vary at least about 0.7 volt to drive actuator 10 from hold to accelerate, the overall amplifier voltage gain from point 88 to point 46 is at least on the order of 3.

Resistor 108, connected between point 88 and the base of transistor 60, provides the initial speed control link described in connection with FIG. 1. It couples a portion of the voltage at point 88 to the non-inverting differential amplifier 16 input. (See item 11 of FIG. 1) For a given vehicle speed (and a given voltage at point 88) the system will operate actuator 10 to vary the position of shaft 22 until the voltage at the arm of potentiometer 70 feeds a voltage into the inverting input of the differential amplifier 16 to match. Thus this link will hold the vehicle throttle at a position that produces the desired speed analog voltage at point 88.

It will be noted that a fraction of the voltage at point 88 is connected to the bottom end of potentiometer 70. The fraction is determined by the ratio of resistors 106 and 72. In a typical circuit the ratio of the value resistor 72 to the sum of the values of resistors 72 and 106 is about 0.3 or 30%. Clearly this fraction will have a greater proportional effect at the idle position of the throttle than it does at higher speeds. This has the ef' feet of changing system gain with speed. The system pa- 1 rameters for the preferred embodiment were selected so that the speed change required to move the throttle to full was 3.8 mph. at 30 mph, 3.5 mph. at mph. and 3.2 mph. at 85 mph. Thus the desired characteristic of greater sensitivity at high speed is achieved. This is done while maintaining a large available dynamic range even at the higher speeds. For example the voltage across potentiometer 70 is about 5.6 volts at zero speed and this drops to only about 5 volts at speeds over 85 mph.

The following list of components represents a set of values that provided the described performance of the circuit of FIG. 2.

Transistor 4O 2N30l9 Transistor 41 2N3019 Resistor 42 100 Ohms Diode 43 1N4002 Diode 44 1N4002 Diode 45 1N4002 Transistor 5O 2N3019 Resistor 51 680 Ohms Resistor 52 1.5K Ohms Resistor 53 33K Ohms Capacitor 54 0.1 microfarad Resistor 55 22K Ohms Transistor 56 2N2904A Resistor 57 6.8K Ohms Resistor 58 12K Ohms Transistor 59 2N3019 Transistor 60 2N3019 Resistor 61 2.7K Ohms Resistor 62 12K Ohms Resistor 63 1K Ohms Resistor 64 8.2K Ohms Resistor 65 8.2K Ohms Resistor 66 150K Ohms Resistor 67 100K Ohms Resistor 68 15K Ohms Resistor 69 27K Ohms Potentiometer 70 5K Ohms Resistor 71 820 Ohms Resistor 72 1.5K Ohms Diode 73 1N4659 Resistor 74 120 Ohms Resistor 100K Ohms Resistor 81 82K Ohms Capacitor 82 20 microfarads IGFIET 85 MFE3004 (Motorola) Resistor 86 2.2K Ohms Capacitor 87 .01 microfarad (polystyrene) Transistor 90 2N3019 Transistor 91 2N3019 Transistor 92 2N3019 Transducer 93 2.2 I-lz/m.p.h. Resistor 94 8.2K Ohms Resistor 95 2.7K Ohms Capac tor 96 220 picofarads Capac tor 97 0.15 microfarad Capacitor 98 5 microfarads Diode 99 1N4002 Diode 100 1N4002 Resistor 101 27K Ohms Resistor 102 20K Ohms Themnstor 103 10K Ohms at 25C. Capacitor 104 5 microfarads Resistor 105 12K Ohms Resistor 106 3.3K Ohms Capacitor 107 0.1 microfarad While the improved speed control has been described, and a set of component values shown for the preferred embodiment, alternatives will occur to persons skilled in the art. Accordingly it is intended that the invention be limited only by the following claims.

We claim:

1. A vehicular speed control system for use in a vehicle having a throttle controlled engine and vehicle speed sensing means, said system comprising:

electromechanical actuator means for operating said throttle to vary the speed of said vehicle through the action of said engine,

means for generating a first electrical quantity in response to the position of said actuator and in direct proportion to the motion that will result in throttle advance,

an amplifier adapted to operate said actuator,

means for applying at least a portion of said first electrical quantity to said amplifier,

means for connecting said amplifier to said actuator in a polarity sense to cause said first electrical quantity to be varied by the action of said actuator and said throttle in a direction which will oppose any change in said first electrical quantity caused by changes in speed of said vehicle,

means for generating a second electrical quantity proportional to the speed of said vehicle, said generating means producing a voltage that varies in linear proportion to vehicle speed, means for establishing and storing a third electrical quantity representative of a desired vehicle speed, means for comparing said second and said third electrical quantities to produce an error quantity representative of the difference between desired and actual vehicle speeds, means for applying said error quantity to said amplifier in a polarity sense that will operate said system to reduce said error, and

means for applying a portion of said second electrical quantity to said amplifier in a polarity such that it opposes said first electrical signal.

2. The system of claim 1 wherein said first electrical quantity is varied as a function of said second electrical quantity, said variation of said first electrical quantity for a given variation of said second electrical quantity being greater at low speeds than it is at high speeds. 

1. A vehicular speed control system for use in a vehicle having a throttle controlled engine and vehicle speed sensing means, said system comprising: electromechanical actuator means for operating said throttle to vary the speed of said vehicle through the action of said engine, means for generating a first electrical quantity in response to the position of said actuator and in direct proportion to the motion that will result in throttle advance, an amplifier adapted to operate said actuator, means for applying at least a portion of said first electrical quantity to said amplifier, means for connecting said amplifier to said actuator in a polarity sense to cause said first electrical quantity to be varied by the action of said actuator and said throttle in a direction which will oppose any change in said first electrical quantity caused by changes in speed of said vehicle, means for generating a second electrical quantity proportional to the speed of said vehicle, said generating means producing a voltage that varies in linear proportion to vehicle speed, means for establishing and storing a third electrical quantity representative of a desired vehicle speed, means for comparing said second and said third electrical quantities to produce an error quantity representative of the difference between desired and actual vehicle speeds, means for applying said error quantity to said amplifier in a polarity sense that will operate said system to reduce said error, and means for applying a portion of said second electrical quantity to said amplifier in a polarity such that it opposes said first electrical signal.
 2. The system of claim 1 wherein said first electrical quantity is varied as a function of said second electrical quantity, said variation of said first electrical quantity for a given variation of said second electrical quantity being greater at low speeds than it is at high speeds. 